Various articles, including biomedical devices, are formed of organosilicon-comprising materials. One class of organosilicon-comprising materials useful for biomedical devices, such as soft contact lenses, is hydrogel materials comprising silicones. A hydrogel is a hydrated, cross-linked polymeric system that contains water in an equilibrium state. Hydrogel contact lenses offer relatively high oxygen permeability as well as desirable biocompatibility and comfort. The inclusion of a silicone, i.e., a siloxy unit containing material, in a hydrogel formulation is the presence of siloxy units in the polymerized material of a device generally provides higher oxygen permeability since silicone based materials have higher oxygen permeability than water.
Organosilicon-comprising materials useful for biomedical devices, including contact lenses, are disclosed in the following U.S. patents: U.S. Pat. No. 4,208,506 (Deichert et al.); U.S. Pat. No. 4,686,267 (Ellis et al.); U.S. Pat. No. 5,034,461 (Lai et al.); and U.S. Pat. No. 5,070,215 (Bambury et al.).
U.S. Pat. Nos. 5,358,995 and 5,387,632 describe hydrogels made from various combinations of silicone macromers, TRIS, n-vinyl pyrrolidone (NVP) and DMA. Replacing a substantial portion of the silicone macromer with TRIS reduced the modulus of the resulting hydrogels. Two publications from the same author, “The Role of Bulky Polysiloxyalkyl Methacrylates in Polyurethane-Polysiloxane Hydrogels”, J. Appl. Poly. Sci., Vol. 60, 1193-1199 (1996), and “The Role of Bulky Polysiloxyalkyl Methacrylates in Oxygen-Permeable Hydrogel Materials”, J. Appl. Poly. Sci., Vol. 56, 317-324 (1995) also describe experimental results indicating that the modulus of hydrogels made from reaction mixtures of silicone-macromers and hydrophilic monomers such as DMA decreases with added TRIS. The addition of methacryloxypropyltris(triethykiloxy)silane (TRIS) reduced the modulus of such hydrogels, but in many examples the modulus is still higher than may be desired.
U.S. Pat. No. 4,208,506 describes monomeric polyparaffinsiloxanes capped with activated unsaturated groups and polymers and copolymers thereof. The monomers of U.S. Pat. No. 4,208,506 are cross-linkers. However, there still remains a need in the art for new monomers to provide silicone hydrogels which are soft enough to make soft contact lenses, which possess additional desirable properties such as high oxygen permeability, suitable water content, and sufficient elasticity, and are comfortable to the contact lens wearer. Prior to the invention as claimed herein, hydrolytically resistant polymeric silicon comprising hydrogel materials have been limited to those comprising at least one siloxane unit, i.e., -[silyl-siloxy]-. Therefore, there is a need for a new type of siloxy comprising unit for producing hydrolytically resistant polymeric silicon comprising materials. That need is addressed by the invention as claimed herein.